In existing communications systems of Wideband Code Division Multiple Access (W-CDMA), Global System for Mobile communications, and the like, a center frequency of frequency bands used for communications is determined to coincide with a predetermined frequency called a raster or a frequency raster. The frequency rasters are arranged, for example, every 200 kHz on a frequency axis.
Therefore, a mobile station can identify the center frequency of an operator and thus connect to a downlink by searching for the frequency rasters by turns on the frequency axis (searching every 200 kHz). Downlink cell search is described in Keiji TACHIKAWA, “W-CDMA mobile communications method”, Maruzen, Inc., pp. 35-45.